Technical guide, , by Green Automatica engineering team · 2 min read
The true cost of running your factory on a diesel generator
Fuel is only part of the bill. Here is how to work out what each kilowatt-hour from your generator really costs, with current Kenyan diesel prices and a worked example.
For many factories outside the main grid, the diesel generator is the heartbeat of production. It is also, very often, the single biggest cost the owner never fully measures. Fuel is bought in cash, maintenance is booked separately and downtime is hidden in lost output. Put together, the numbers are usually much higher than anyone expects.
Start with fuel: what one kilowatt-hour costs
A diesel generator running at a healthy load burns roughly 0.3 litres of fuel for every kilowatt-hour it produces. When a large generator runs lightly loaded, which is common at night or between shifts, consumption per kWh rises noticeably.
In the pricing cycle from 15 October to 14 November 2026, the maximum pump price for diesel in Nairobi was KES 227.76 per litre (EPRA). Sites far from Nairobi pay more once transport is added.
| Worked example (estimate) | Value |
|---|---|
| Fuel used per kWh | 0.3 litres |
| Diesel price | KES 228 per litre |
| Fuel cost per kWh | 0.3 × 228 ≈ KES 68 |
| Factory using 300 kWh a day, 26 days a month | 7,800 kWh |
| Monthly fuel bill | ≈ KES 530,000 |
Then add the costs that never appear on the fuel receipt
- Servicing and parts: oil, filters, injectors and overhauls, usually every few hundred running hours.
- Fuel logistics and losses: transport to remote sites, storage, theft and spillage.
- Downtime: every breakdown or late fuel delivery stops the line. Spoiled raw materials, idle workers and missed orders often cost more than the fuel itself.
- Price risk: fuel prices change every month, so your cost of production does too.
- Emissions and noise: a growing concern for buyers, export markets and green financing.
How solar changes the equation
A solar system has a higher upfront cost but almost no fuel cost. Over its life, a well-designed solar and battery system often delivers energy for less than half of a generator's fuel cost per kWh, and the price is locked in on the day it is installed. The key is designing it around how your factory actually uses power, which is exactly what most partial solar installations miss. See Can a factory run 100% on solar?
Work out your own number in 15 minutes
- Add up the litres of diesel you bought over the last three months.
- Note the generator's running hours over the same period, from the hour meter.
- Add servicing and repair invoices.
- Estimate production lost to generator problems or fuel shortages.
Divide the total by the kWh produced (or estimate it from the load and hours), and you have your true cost of energy. Most owners who do this exercise are surprised.
Frequently asked questions
How much does it cost to run a diesel generator per kWh in Kenya?
At about 0.3 litres per kWh and a diesel price of around KES 228 per litre (Nairobi, October–November 2026), fuel alone costs roughly KES 68 per kWh. Servicing, fuel transport and downtime push the true cost higher.
Can solar completely replace a factory generator?
Yes, for many factories, when solar, battery storage and smart load control are designed together around the real production load. The generator can then be kept only as an emergency backup or removed.
Why does my generator use more fuel at night?
Large generators running at a small fraction of their rating burn more fuel per kWh. Night loads such as security lighting or a few motors are a common cause.